Kinder and his colleagues assessed the prevalence of vitamin D deficiency in a cohort of patients with interstitial lung disease, who are often treated with corticosteroids. The detrimental effect of chronic use of corticosteroids on bone health has been well established, according to the researchers. Of the patients included in the study, 51 had interstitial lung disease and 67 had other forms of interstitial lung disease related to autoimmune connective tissue diseases.
A vitamin D insufficiency was defined as a serum level of less than 30 ng/mL. A level of less than 20 ng/mL was considered deficient. Both insufficient and deficient levels were prevalent in the study. In the overall sample, lower vitamin D levels were associated with reduced forced vital capacity (P=0.01). When the analysis was restricted to patients with connective tissue disease, both forced vital capacity and diffusing capacity of lung for carbon monoxide — a measure of the lung’s ability to transfer gases from the air to the blood — were significantly reduced (P<0.05 for both). After adjustment for several potential confounders — including age, corticosteroid use, race, and season, the presence of connective lung disease was a strong predictor of vitamin D insufficiency (OR 11.8, 95% CI 3.5 to 40.6).
According to the researchers, a pathogenic role of low vitamin D in the development of autoimmune diseases such as interstitial lung disease is plausible because of the immunoregulatory role of the biologically active form of vitamin D, 1,25-(OH)2D. “All cells of the adaptive immune system express vitamin D receptors and are sensitive to the action of 1,25-(OH)2D,” they wrote. “High levels of 1,25-(OH)2D are potent inhibitors of dendritic cell maturation with lower expression of major histocompatibility complex class II molecules, down-regulation of costimulatory molecules, and lower production of proinflammatory cytokines.” “A common theme in the immunomodulatory functions of vitamin D is that higher levels are immunosuppressive,” they continued, “which is consistent with a potential role for hypovitaminosis D in the pathogenesis of autoimmune disorders.”
In a statement, Len Horovitz, MD, a pulmonary specialist at Lenox Hill Hospital in New York City, commented that “vitamin D is known to promote wound healing, and to benefit the immune system. So it is not surprising to find that patients with immune lung disorders are vitamin D deficient.” He said that all of his patients are screened and treated for vitamin D deficiency with supplements. The study authors noted that further research is needed to determine whether supplementation is associated with improved outcomes. The study was limited, Kinder and his colleagues wrote, by its use of patients from a single center in Cincinnati.
In addition, the cross-sectional design of the study did not evaluate whether vitamin D supplementation is associated with any improved clinical outcomes. To examine that issue, the team called for prospective controlled interventional studies to determine whether vitamin D7 supplements can ameliorate symptoms and improve outcomes in connective tissue disease-related interstitial lung disease.
Source reference: Hagaman J, et al “Vitamin D deficiency and reduced lung function in connective tissue-associated interstitial lung diseases” Chest 2011; DOI: 10.1378/chest.10-0968.